Sustainable Improvement of Residual Lateritic Soils Using Alum

Cement stabilization has gained popularity in the tropics despite its known side effects. In Nigeria, a developing nation for instance, high cost and negative environmental impacts accompanying the use of cement constitute major drawbacks raising concerns. These shortcomings often make more sustainable alternatives necessary in a depressed economy. The current study explores the effects of alum on swelling potentials and strength of fine-grained Nigerian lateritic soils with a view to ascertaining the viability of the additive as cost-effective, eco-friendly and sustainable substitute for improving engineering properties of the soils as highway embankment or pavement materials. Particle-size analysis and Atterberg limits tests conducted according to British Standards (BS 1377) and ASTM-D4318 respectively, aided in AASHTO classification of the un-treated soils as A-6 (clayey soil), A-4 (silty soil) and A-7-5 (clayey soil). These are poor to fair subgrade materials requiring stabilization. Similarly, high amounts of fines in the natural soils suggest susceptibility to recurring shrink and swell during alternating dry and wet seasons typical of tropical regions. However, alum-treated soils show reduction in plasticity with strong negative correlations. This implies reduction in swelling potentials and improvement in strength with alum treatment. Also, California bearing ratio (CBR) and shear strength, which followed the British Standards indicate strong positive correlations with alum content for the granite- and charnockite-derived soils. This indicates improved strength. Generally, the results suggest that alum has the potential to improve plastic fine-grained lateritic soils in line with the Federal Ministry of Works and Housing general specification for roads and bridges, with combined engineering, economic and environmental benefits. engineering tests were conducted, viz: consistency limits, CBR and Triaxial unconsolidated-undrained tests. The consistency limits tests followed the ASTM-D4318 specifications while the CBR and triaxial tests were conducted in accordance with the British standard, BS 1377 (1990) specifications. For the triaxial unconsolidated-undrained test, confining pressures of 100, 200 and 300 kPa were applied.